/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.sparql.function;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;

import org.apache.jena.atlas.logging.Log;
import org.apache.jena.query.ARQ;
import org.apache.jena.sparql.ARQConstants;
import org.apache.jena.sparql.util.Context;
import org.apache.jena.sparql.util.MappedLoader;
import org.apache.jena.sys.JenaSystem;

public class FunctionRegistry
{
    static { JenaSystem.init(); }

    // Extract a Registry class and do casting and initialization here.
    private Map<String, FunctionFactory> registry = new HashMap<>();
    private Set<String> attemptedLoads = new HashSet<>();

    public static FunctionRegistry standardRegistry() {
        FunctionRegistry reg = get(ARQ.getContext());
        return reg;
    }

    public static void init() {
        // Initialize if there is no registry already set
        FunctionRegistry reg = new FunctionRegistry();
        ARQFunctions.load(reg);
        StandardFunctions.loadStdDefs(reg);
        StandardFunctions.loadOtherDefs(reg);
        set(ARQ.getContext(), reg);
    }

    public static FunctionRegistry get() {
        // Initialize if there is no registry already set
        FunctionRegistry reg = get(ARQ.getContext());
        if ( reg == null ) {
            Log.warn(FunctionRegistry.class, "Standard function registry should already have been initialized");
            init();
            reg = get(ARQ.getContext());
        }

        return reg;
    }

    public static FunctionRegistry get(Context context) {
        if ( context == null )
            return null;
        return context.get(ARQConstants.registryFunctions);
    }

    public static void set(Context context, FunctionRegistry reg) {
        context.set(ARQConstants.registryFunctions, reg);
    }

    /**
     * Copies the origin registry into a new one, or makes a fresh instance if the specified registry is {@code null}.
     * @param from {@link FunctionRegistry } or {@code null}
     * @return {@link FunctionRegistry} a new instance
     */
    public static FunctionRegistry createFrom(FunctionRegistry from) {
        FunctionRegistry res = new FunctionRegistry();
        if (from != null) {
            res.registry.putAll(from.registry);
        }
        return res;
    }

    public FunctionRegistry()
    {}

    /** Insert a class that is the function implementation
     *
     * @param uri           String URI
     * @param funcClass     Class for the function (new instance called).
     */
    public void put(String uri, Class<? > funcClass) {
        if ( !Function.class.isAssignableFrom(funcClass) ) {
            Log.warn(this, "Class " + funcClass.getName() + " is not a Function");
            return;
        }

        put(uri, new FunctionFactoryAuto(funcClass));
    }

    /** Insert a function. Re-inserting with the same URI overwrites the old entry.
     *
     * @param uri
     * @param f
     */
    public void put(String uri, FunctionFactory f) { registry.put(uri,f); }

    /** Lookup by URI */
    public FunctionFactory get(String uri) {
        FunctionFactory function = registry.get(uri);
        if ( function != null )
            return function;

        if ( attemptedLoads.contains(uri) )
            return null;

        Class<? > functionClass = MappedLoader.loadClass(uri, Function.class);
        if ( functionClass == null )
            return null;
        // Registry it
        put(uri, functionClass);
        attemptedLoads.add(uri);
        // Call again to get it.
        return registry.get(uri);
    }

    public boolean isRegistered(String uri) { return registry.containsKey(uri); }

    /** Remove by URI */
    public FunctionFactory remove(String uri) { return registry.remove(uri); }

    /** Iterate over URIs */
    public Iterator<String> keys() { return registry.keySet().iterator(); }

}
